Antibodies are drawing attention as pharmaceuticals as they are highly stable in blood and have few side effects. Of these, a number of IgG-type antibody pharmaceuticals are available on the market and many antibody pharmaceuticals are currently under development (Non-patent Documents 1 and 2).
Almost all antibody pharmaceuticals currently available on the market are of the IgG1 subclass. IgG1-type antibodies are expected be useful as anti-cancer antibody pharmaceuticals since they can bind to Fcγ receptor and exert ADCC activity. However, when it comes to antibody pharmaceuticals intended for neutralizing biological activity of an antigen, binding of the Fc domain to Fcγ receptor, which is important for effector functions such as ADCC, can cause unnecessary side effects, and thus it is preferable to eliminate such binding activity (Non-patent Document 3). Furthermore, since Fcγ receptor is expressed on antigen-presenting cells, molecules that bind to Fcγ receptor tend to be presented as antigens. It has been reported that antigenicity is and can be enhanced by linking a protein or peptide to the Fc domain of IgG1 (Non-patent Document 4 and Patent Document 1). Interaction between the antibody Fc domain and Fcγ receptor is thought to be a cause of the serious side effects encountered in phase-I clinical trials of TGN1412 (Non-patent Document 5). Thus, binding to Fcγ receptor is considered unfavorable in antibody pharmaceuticals intended for neutralizing the biological activity of an antigen from the perspective of side effects and antigenicity.
A method for impairing the binding to Fcγ receptor is to alter the subtype of the IgG antibody from IgG1 to IgG2 or IgG4; however, this method cannot completely inhibit the binding (Non-patent Document 6). However, the binding to Fcγ receptor is not completely inhibited even if IgG2 or IgG4 is used. One of the methods reported for inhibiting the binding to Fcγ receptor is to artificially alter the Fc domain. For example, the effector functions of anti-CD3 antibodies and anti-CD4 antibodies cause side effects. Thus, amino acids that are not present in the wild-type sequence were introduced into the Fcγ-receptor-binding domain of Fc (Non-patent Documents 3 and 7), and clinical trials are currently being conducted to assess anti-CD3 antibodies and anti-CD4 antibodies that have a mutated Fc domain and do not bind to Fcγ receptor (Non-patent Documents 5 and 8). Alternatively, Fcγ receptor-nonbinding antibodies can be prepared by altering the FcγR-binding sites of IgG1 (positions 233, 234, 235, 236, 327, 330, and 331 in the EU numbering; hereafter abbreviated as position X (EU numbering)) to an IgG2 or IgG4 sequence (Non-patent Document 9 and Patent Document 2). However, there are no reports of constant regions that have completely lost binding to all FcγRs (FcγRI, FcγRIIa, and FcγRIIIa). From the perspective of side-effects, the present inventors constructed constant regions that have completely lost binding to all FcγRs.
Documents of related prior arts for the present invention are described below.